Exercise enthusiasts use treadmills that convey, on an endless track, a surface upon which they may run, jog or walk in place. Treadmills typically have a conveyor belt that rotates around a front and a rear roller assembly. Normally, each roller assembly has a fixed shaft with an outer tube disposed around it. The outer tube rotates on bearing assemblies which are supported by the fixed shaft. The bearing assemblies are typically ball bearing systems that comprise an inner and outer race, a series of balls and a cage to support the balls.
In order to eliminate slippage when users are stepping on the conveyor belt, the conveyor belt is put into tension. The tensioning of the belt causes the fixed shafts of the roller assemblies to bend or “arc” towards each other. The bending in the center of the shaft causes the ends of the shaft to deflect in the opposite direction. This deflection causes the ends of the ends of the shafts to exert an excessive pressure on the inner race of the bearing assemblies. The excessive pressure often causes the ball bearings and the races to become brittle. Thus, the bearing assemblies may be easily damaged and chipping and brinnelling may occur. Brinnelling is a denting of the race following an excessive load. This brinnelling, although it has no major effect on life, but at comparatively light loads, causes a great increase in noise. On the other hand, chipping of the hardened brittle ball bearings will eventually lead to bearing noise, roughness, and ultimately failure.
Most treadmills, in a certain price range, use similar front and rear rollers as described above. Shaft arcing in rollers has been a problem for many years. Recently, shaft arcing has been reduced by increasing the diameter of the shaft. However, it is often cost prohibitive to use shafts with large enough diameters to completely eliminate arcing. What is needed, therefore, is a means of distributing the loads within the roller apparatus that will reduce pressure and resistance on the bearing members.